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Liquids as a class often behave in a similar way in the phonotactics of a language: for example, they often have the greatest freedom in occurring in consonant clusters.[1] In some languages, such as Japanese and Korean, there is one liquid phoneme which may have both lateral and rhotic allophones.[1]

English has two liquid phonemes, one lateral, /l/ and one rhotic, /ɹ/, exemplified in the words led and red.

Many other European languages have one lateral and one rhotic phoneme. Some, such as Greek, Italian and Serbo-Croatian, have more than two liquid phonemes. These three languages have the set /l/ /ʎ/ /r/, with two laterals and one rhotic. Similarly, the Iberian languages contrast four liquid phonemes. /l/, /ʎ/, /ɾ/, and a fourth phoneme that is an alveolar trill in all but Portuguese, where it is a guttural trill or fricative. Some European languages, like Russian and Irish, contrast a palatalized lateral–rhotic pair with an unpalatalized (or velarized) set (e.g. /lʲ/ /rʲ/ /l/ /r/ in Russian).

Elsewhere in the world, two liquids of the types mentioned above remains the most common attribute of a language's consonant inventory, except in North America and Australia. In North America, a majority of languages do not have rhotics at all and there is a wide variety of lateral sounds—though most are obstruent laterals rather than liquids. Most indigenous Australian languages are very rich in liquids, with some having as many as seven distinct liquids. These typically include dental, alveolar, retroflex and palatal laterals, and as many as three rhotics.

On the other side, there are many indigenous languages in the Amazon Basin and eastern North America, as well as a few in Asia and Africa, with no liquids.

The grammarian Dionysius Thrax used the Greek word ὑγρός (hygrós, "moist") to describe the /l,r,m,n/phonemes of classical Greek.[3] Most commentators assume that this referred to their "slippery" effect on meter in classical Greek verse when they occur as the second member of a consonant cluster.[3] This word was calqued into Latin as liquidus, whence it has been retained in the Western European phonetic tradition.